Examples of information for uniquely specifying a device such as a server device on a network include name information (logical name) such as a fully qualified domain name (FQDN) and a netbios name and address information, such as an IP address, which is unique to a device. Here, address information such as an IP address is static and it is not easy to make a change of the address information. Therefore, a device name is commonly specified by name information such as a FQDN and a netbios name in communication, the name information is converted into address information such as an IP address by utilizing name resolution such as a domain name system (DNS) and Windows (a registered trade mark) Internet Name Service (WINS), and communication with the device is started by using the address information. In the DNS, for example, when a client requests name resolution for a FQDN from a DNS server which is specified by a LAN and a WAN, the DNS server device tracks a hierarchy from a route server device of the DNS or requests name resolution from a server device of an upper stage, for example, so as to be able to return an IP address corresponding to the FQDN to the client (refer to Patent Literature 1).
Meanwhile, a cloud-key management type encryption for solving a key management issue of a decryption key (for example, a symmetric key in a case of a symmetric key crypto system and a private key in a case of a public key cryptosystem) is proposed and the general description of the system (cloud key system) is disclosed by a literature and the like (refer to Non-Patent Literature 1).